1. Technical Field
The present disclosure is generally related to scene projection/generation systems and methods and, more particularly, is related to hyperspectral scene projection/generation systems and methods.
2. Description of the Related Art
Hyperspectral scene projection/generation systems can be used for projection and generation of hyperspectral scenes, which provide, among other benefits, insight into the ability to detect and identify minerals, terrestrial vegetation, and man-made materials and backgrounds at various wavelengths. Actual detection of materials may be dependent on the spectral coverage, spectral resolution, and signal-to-noise ratio of the system, in addition to the abundance of the material and the strength of absorption features for that material in the wavelength region of interest.
Current hyperspectral scene projection/generation systems typically comprise traditional dispersive elements, such as gratings and prisms, that are rotated and/or moved over a defined period of time in order to generate a hyperspectral scene. FIGS. 1A-1B illustrate an exemplary hyperspectral scene projection/generation system 10 that comprises imaging elements or imager configured such that there is relative motion between a scene and the imager elements. The hyperspectral scene projection/generation system 10 comprises a light source 12 that generates a scene (e.g., a pixellated, 2-spatial dimensional (2D) triangle as shown) comprising white light that includes a mixture of wavelengths through the use of well-known systems and methods. The scene may comprise any two (or more) spatial dimensional collection of objects that is to be imaged. Such a light source 12 may comprise a pixellated light source, such as an exemplary light source described further in U.S. Pat. No. 6,485,150, herein incorporated by reference. The hyperspectral scene projection/generation system 10 further comprises a slit or thin aperture 14, a grating 16 (or prism), an imaging lens 18, and a display system 20. The display system 20 may be configured as a screen on which an imaged scene may be projected, a camera, and/or a video monitor, among other devices or systems on which an imaged scene may be captured and/or displayed.
The light source 12 provides beams of light corresponding to the generated scene that passes through the slit 14 to the grating 16. All of the colors of the imaged scene, as seen through the slit 14, are diffracted from the grating 16 as it is moved, resulting in the formation of the image of the slit 14 on the display system 20. The display system 20, for example, may comprise a camera or detector array coupled to a digital computer to digitize the image and store it and display it on a video monitor. Since there is relative motion between the scene and the imaging system (e.g., the slit 14, the grating 16, the lens 18 and the display system 20) as a function of time, for example t1-t6 (this relative movement, for example, represented symbolically by the two headed arrow under the scene), a progressively more complete image of the scene (which includes all of the colors of the imaged scene) is displayed on the display system 20 as time progresses. Scene images 22, 24, 26, 28, 30, and 32 are generated at respective times t1, t2, t3, t4, t5, and t6. Each scene image comprises columns, each proportioned to the dimension of the slit 14, of each respective color of the incident white length (e.g., scene). For example, in scene image 22 at time t1, “r” represents the color red at a wavelength (λ1), “o” represents the color orange at wavelength (λ2), and so on until the color violet (“v”) at wavelength (λn). In other words, using a 2-D detector array for the display system 20, one dimension recorded is the spatial dimension of the slit and the other dimension recorded is the wavelength or color due to dispersion. In recording these partial scene images at each time (t1-t6), the position of pixels corresponding to the different colors can be recorded. That is, as shown, different colors are incident on different columns of pixels, so the color information of the scene image has a column association.
Thus, in one exemplary operation, at time t1, a first partial image 22 of the scene is formed on the camera, stored on the computer, the extent of the first partial image generated in proportion to the dimensions of the slit 14 (i.e., a one spatial dimension (herein, 1-D) image). At time t2, a second partial image of the scene is generated, corresponding to another slit dimension to the first image but covering a different portion of the scene due to the movement of the imager. Assuming the display system 20 comprises a camera connected to a digital computer, at a time corresponding to t2, the first partial scene 22 stored in memory of the computer may be combined with the second partial scene 24 during the image cube formation stage, as explained below. This process of relative movement and partial scene image recording continues in ordered sequence from t3, t4, t5, and t6 corresponding to image scenes 26, 28, 30, and 32 (i.e., the wavelengths are in sequential order as a consequence of the diffraction from the grating 16) until the complete scene image covering the entire spectrum is covered.
The left hand side of FIG. 1B shows the series of partial scene images 22-32 generated through the above-described operation shown in FIG. 1A. The right hand side of FIG. 1B illustrates an exemplary process for generating a full image cube 50 of 2-D scene images 52, 54, 56, 58, 60, and 62, each scene image at a respective color of the white light spectrum (versus the partial scene images 22-32, each spanning every color of the white light spectrum). The display system 20 (e.g., computer portion) adds the pixel column values from each partial scene image to generate a full 2-D scene image at the respective color or wavelength. Thus, the result of the computations within the display system 20 is the generation and display of individual, 2-D (-x or -t, and -y), spectral scene images generated at each wavelength (λ1, λ2, λn), as illustrated by the dimension axis 70. Desired wavelengths of the full-color scene image are then selected to provide the hyperspectral scene projection/generation functionality for individual wavelengths. However, such conventional systems typically require moving parts, large and time-consuming computing requirements (e.g., storing, processing, sorting, etc.) to retrieve a desired spectral scene image, and/or local control. Such systems are also inflexible due at least in part to requiring the collection of each scene image at each wavelength to generate a desired spectral scene image.